Communication system providing hybrid optical/wireless communications and related methods

ABSTRACT

A communication system includes at least one optical-wireless device coupled to a longitudinal side of an optical fiber. The optical-wireless device may include an optical fiber power unit for converting optical power into electrical power, and a wireless communication unit electrically powered by the optical fiber power unit. The optical-wireless device may include a substrate mounting the optical fiber power unit and the wireless communication unit to the longitudinal side of the optical fiber. The wireless communication unit may include a radio frequency transmitter, and a signal optical grating coupling the transmitter to the longitudinal side of the optical fiber. The radio frequency transmitter in some embodiments may include an ultra-wideband transmitter. A dipole antenna may also be provided including first and second portions extending in opposite directions along the longitudinal side of the optical fiber.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of communications,and, more particularly, to a communication system, devices andassociated methods for hybrid optical/wireless communications andconversions.

BACKGROUND OF THE INVENTION

[0002] Communications systems are often used to route data, voice,and/or video signals among users. One typical communications system isthe Local Area Network (LAN) that interconnects a plurality of computerworkstation users. Perhaps the most common way in which computers orother devices are connected together in a LAN is through electricallyconductive wires. For example, wall or floor connectors may be locatedthroughout a building to which computer workstations are connected, andmetal wires are run from the wall connectors to one or more centrallocations where they may be connected to centralized computing devices,such as a server.

[0003] Certain disadvantages may accompany the use of wired networks.For instance, because electrical power is being transmitted over thewires, the installation of the wires may be subject to electrical codesthat may make installation more difficult or even costly. Furthermore,the bandwidth that is available using typical metal wires (e.g., copperwires) may be less than desirable for some applications.

[0004] As a result of such limitations, other types of interconnectionshave been utilized in an attempt to provide “copperless” networks. Forexample, fiber-optic lines allow light signals which correspond toelectrical signals to be transmitted between computers or other devicesat a very high rate and bandwidth. Yet, fiberoptic communication isoften more expensive than wires, and thus running fiber-optic lines tonumerous wall connectors may be cost prohibitive in some circumstances.

[0005] Further, fiber-optic cables may be more difficult to extractsignals from than wires. As a result, various approaches for addressingthe difficulties of signal extraction from optical fibers have beendeveloped. One such approach is disclosed in U.S. Pat. No. 6,265,710 inwhich light emerging from an optical fiber is directed by focusingelements at a photodetector or at the input face of another glass fiber.Another approach is to use gratings which are physically configured tocapture light of a particular wavelength. An example of this approach isdisclosed in U.S. Pat. No. 6,304,696 to Patterson et al.

[0006] Another way to interconnect one or more devices in a LAN is touse wireless communications links. For example, each device in the LANmay include a wireless radio frequency (RF) transceiver for sending andreceiving data signals to other devices using one or more designatedfrequencies. While this approach has the advantage of requiring less, ifany, wall connectors than a wired or fiber-optical network, the wirelesscommunications links may be subject to interference, signal distortion,or signal loss as devices are moved to various locations.

SUMMARY OF THE INVENTION

[0007] In view of the foregoing background, it is therefore an object ofthe invention to provide a communication system that effectively usesthe advantages of optical fiber and wireless communication.

[0008] This and other objects, features and advantages in accordancewith the present invention are provided by a communication systemincluding an optical fiber, and at least one optical-wireless devicecoupled to a optical fiber. By way of example, the at least oneoptical-wireless device may be coupled to the fiber by standard fiberconnectors, microfabrication of grating structures within the fiber,surface polished fiber to serve as an electronic substrate, etc.Moreover, the optical-wireless device may include an optical fiber powerunit coupled to the optical fiber for converting optical power thereininto electrical power, and a wireless communication unit electricallypowered by the optical fiber power unit and coupled to the opticalfiber. The optical-wireless device may include a substrate mounting theoptical fiber power unit and the wireless communication unit to thelongitudinal side of the optical fiber.

[0009] The optical fiber power unit may include a photovoltaic deviceand a power optical grating coupling the photovoltaic device to thelongitudinal side of the optical fiber. The wireless communication unitmay include a radio frequency transmitter, and a signal optical gratingcoupling the transmitter to the longitudinal side of the optical fiber.

[0010] In accordance with another important aspect of the invention, theradio frequency transmitter may be an ultra-wideband transmitter. Theultra-wideband transmitter, in turn, may include an optical detectorhaving an input coupled to the signal optical grating; an amplifierhaving an input connected to the output of the optical detector; apseudorandom code generator; a multiplier having inputs connected to theoutputs of the amplifier and pseudorandom code generator; and a pulsegenerator having an input connected to the output of the multiplier.

[0011] The ultra-wideband transmitter may also include an antennaconnected to the output of the pulse generator. By way of example, theantenna may be a dipole antenna. For a particularly compact andefficient construction, the dipole antenna preferably includes first andsecond portions extending in opposite directions along the longitudinalside of the optical fiber.

[0012] The optical fiber may include a core and a cladding surroundingthe core. Accordingly, the optical fiber power unit and the wirelesscommunication unit may be coupled to the core of the optical fiber.

[0013] In those embodiments where the wireless communication unitincludes a wireless transmitter, the system may further include at leastone wireless receiver spaced from the wireless transmitter and receivingsignals therefrom. Conversely, in those embodiments where the wirelesscommunication unit comprises a wireless receiver, the system may alsoinclude at least one wireless transmitter spaced from the wirelessreceiver and transmitting signals thereto. Of course, in yet otherembodiments, duplex communications may be provided.

[0014] The communication system is particularly applicable to copperlessnetworks. In these embodiments, the at least one optical-wireless devicemay be a plurality of optical-wireless devices coupled to the opticalfiber at spaced apart locations along the longitudinal side of theoptical fiber. In some situations, a plurality of optical-wirelessdevices can be coupled to the optical fiber.

[0015] Different optical wavelengths may be used for powering andsignals in the optical-wireless device. More particularly, the wirelesscommunication unit may operate at a first optical wavelength, and thesystem may include an optical power source coupled to the optical fiberfor powering the optical fiber power unit and operating at a secondwavelength different than the first optical wavelength. Additionally,instead of different optical wavelengths, the optical-wireless devicescould also operate from different modes, polarizations, codes, orotherwise differentiate signals and power between the optical-wirelessdevices.

[0016] A method aspect of the invention is for optical-wirelesscommunication. The method may include coupling at least oneoptical-wireless device to a longitudinal side of an optical fiber,where the at least one optical-wireless device may include an opticalfiber power unit and a wireless communication unit connected thereto.The method may also include supplying optical power into the opticalfiber, converting the optical power in the optical fiber into electricalpower using the optical fiber power unit, and electrically powering thewireless communication unit for optical-wireless communication using theelectrical power converted from the optical power. In addition, externalpower could be supplied by methods such as solar cells, rectifyingantennas, or by electrical wire, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic diagram of a communication system accordingto the present invention including a plurality of optical-wirelessdevices coupled to an optical fiber.

[0018]FIG. 2 is partial cross-sectional view illustrating one embodimentof an optical-wireless device and the optical fiber of FIG. 1 in greaterdetail.

[0019]FIG. 3 is a schematic block diagram of an ultra-widebandtransmitter and power generation circuitry therefor for theoptical-wireless device of FIG. 2.

[0020]FIG. 4 is a perspective view illustrating mounting of an alternatearrangement of the optical-wireless device of FIG. 2 on the opticalfiber.

[0021]FIG. 5 is a schematic block diagram illustrating communicationsbetween an optical-wireless device according to the invention includingan ultra-wideband transmitter and a receiver.

[0022]FIG. 6 is a schematic block diagram illustrating communicationsbetween a transmitter and an optical-wireless device according to theinvention including an ultra-wideband receiver.

[0023]FIG. 7 is a flow diagram illustrating a method according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout, andprime notation is used to indicate similar elements in alternativeembodiments.

[0025] Referring initially to FIG. 1, a communication system 10according to the present invention illustratively includes an opticalfiber 11, and at least one optical-wireless device 12 coupled to apoint(s) along a longitudinal side of the optical fiber. In the contextof a LAN, for example, the optical fiber 11 may be connected to a server16 or other central data source/node to which electronic devices such aspersonal data assistants 13, cellular telephones 14, and/or personalcomputers (PCs) 15 require access. Of course, those of skill in the artwill appreciate that the communication system 10 of the presentinvention may be used in numerous other applications other than LANs,and also with other types of electronic devices.

[0026] As such, those of skill in the art will appreciate that thecommunication system 10 is particularly applicable to copperlessnetworks. In such embodiments, a plurality of optical-wireless devices12 a, 12 b, 12 c may be coupled to the optical fiber 11 at spaced apartlocations along the longitudinal side of the optical fiber. Theoptical-wireless devices 12 a, 12 b, 12 c are used for respectivelyproviding wireless communications with the personal data assistant 13,the cellular telephone 14, and the personal computer (PC) 15. As will bediscussed more fully below, the optical-wireless device 12 mayadvantageously be used to convert optical signals sent on the opticalfiber 11 (e.g., by the server 16) to wireless signals and transmit thesame to a respective electronic device. Conversely, the optical-wirelessdevice 12 may also convert wireless signals sent from a respectiveelectronic device to corresponding optical signals and send the same onthe optical fiber 11 (e.g., to the server 16), as illustratively shownwith arrows in FIG. 1.

[0027] As a result of the optical-wireless device 12 of the presentinvention, the communication system 10 may advantageously realizecertain advantages of both optical and wireless communications whileavoiding some of their respective drawbacks. More particularly, one ormore optical fibers 11 may be used to route signals from a server 16 orother central data source throughout an entire physical network area(e.g., a floor of a building, a ship, etc.) without having to runoptical fibers to numerous workstation connection points.

[0028] Further, because optical signals can travel relatively longdistances over optical fibers with minimal degradation, the range overwhich the communication system 10 extends may be much larger than thatof a purely wireless network, and may even extend between buildings,etc., without the need for wireless signal repeaters. Plus, since thewireless signals transmitted between the optical-wireless device 12 anda respective electronic device generally do not have to travel as far asin a purely wireless network (i.e., they only have to travel to thenearby optical fiber 11 and not all the way to the server 16),interference and signal degradation may potentially be reduced as well.

[0029] Turning now more particularly to FIGS. 2-4, the optical-wirelessdevice 12 will now be described in greater detail. The optical fiber 11may include a core 23 and a cladding 24 surrounding the core, as will beappreciated by those of skill in the art. The optical-wireless device 12may include an optical fiber power unit 20 coupled to the core 23 forconverting optical power therein into electrical power, as will bedescribed further below.

[0030] Further, a wireless communication unit 25 may also be coupled tothe core 23 of the optical fiber 11 and electrically powered by theoptical fiber power unit 20. In some embodiments, such as the oneillustrated in FIG. 2, portions of the optical fiber power unit 20 andthe wireless communication unit 25 may be embodied in a singleintegrated device. A dotted line is therefore shown in FIG. 2 to aid inillustrating that the two separate functions are performed in the sameoptical-wireless device 12, although no particular segmentation orarrangement of the various circuit components is required.

[0031] The optical fiber power unit 20 may include one or morephotovoltaic devices 21 and a respective power optical grating 22designed specifically to extract light from the core 23 of the opticalfiber 11 to be used for power generation. As such, the power opticalgrating 22 is preferably “tuned” to extract light having a particularoptical wavelength λ₁ from the core 23, which is converted to electricalpower for the wireless communications device 25. As will be appreciatedby those skilled in the art, a micro-optic structure to extract lightfor power generation may be “tuned” to specific wavelengths,polarizations, modes, etc. The optical fiber power 20 unit 20 mayoptionally include additional power conditioning circuitry as required,as will be appreciated by those of skill in the art, which isschematically shown in FIGS. 5 and 6.

[0032] By way of example, one particular type of photovoltaic device 21which may be used is a relatively large-area planar-diffused InGaAsphotodiode with a broadband anti-reflection coating on thephotosensitive surface. Such diodes are known to those of skill in theart. Several such photovoltaic diodes 21 may be connected in series(illustratively shown in FIGS. 5 and 6) to generate the requisitevoltage to power the wireless communication unit 25 and reverse bias anoptical signal detector 26 thereof (discussed further below). Thephotodiodes 21 are preferably placed over respective gratings 22 in amanner that optimizes the illumination efficiency.

[0033] As will be appreciated by those of skill in the art, to optimizethe illumination efficiency of a photodiode it is important to have themaximum amount of light extracted from the core 23 absorbed within thedepletion region of the photodiode 21. Light extracted from the core 23and not absorbed in the depletion region represents loss and a reductionin efficiency. Losses can result from reflections, misdirected ormisfocused light, and absorption of photons outside the depletionregion. Anti-reflection coatings, junction orientation, and beamfocusing may be tailored in a particular design application to minimizelosses, as will also be appreciated by those skilled in the art.

[0034] One exemplary approach for illuminating a photodiode 21 is tohave the light incident normal to the photodiode junction. An alternateapproach would be to have the incident light parallel to the photodiode21 junction. The latter approach has the advantage of aligning thejunction along the length of the core 23. This may accommodate longergratings 22 with enhanced functionality, for example. Other approachesmay potentially be used as well, as will be understood by those skilledin the art.

[0035] It will also be understood that for maximum power delivery to aload from a power source, load resistance and equivalent sourceresistance is preferably made equal. Under illumination, a photodiodeconnected to an open circuit load will produce a photovoltage, V_(OC).Likewise, a photodiode connected to a short circuit load will produce aphotocurrent, ISC. The equivalent source resistance, REQ, of thephotodiode is then approximately V_(OC)/I_(SC). To optimize powerdelivery to the optical-wireless device 12, the source resistance andload resistance should preferably be tailored in each particularapplication to achieve an optimal match, as will be appreciated by thoseskilled in the art.

[0036] In addition to optimizing illumination of the photodiodes,parasitic impedances introduced by the packaging into the electricalinterconnect should preferably be held to a minimum. Parasiticresistance in the power source conductors will decrease power conversionefficiency, as will be appreciated by those of skill in the art. Caremay also need to be taken to ensure that parasitic impedances betweenthe transmitter 27 and antenna 34 (FIG. 3) do not overly limit thebandwidth and/or shape of the radiated pulses. Various types ofinterconnections may be used in accordance with the present invention,and potential criteria for the selection thereof are that they should besimple, inexpensive, and accommodate mass production.

[0037] One such approach for forming the electrical interconnections isto use conductive epoxy. Forming interconnections in this manner is wellknown in the art, has lower parasitic inductance than wire bonding, andoccupies less physical space than other conventional interconnections.The same epoxy forming the interconnect can also permanently hold thedevices in place. In addition, additives can be used to alter theconductivity of the epoxy to form a resistor 39 (FIG. 3) used to biasthe signal detecting diode 26. This is possible because of the very lowpower requirements of the biasing resistor 39 in the signal detectorcircuit. Further, non-conductive epoxy 44 may be used to isolate thephotodiodes 21 form the signal detecting diode(s) 26.

[0038] Multifunctional use of epoxy may reduce package complexity, size,the number of process steps required for assembly, and cost. Where wirebonds are more appropriately used, the parasitics associated therewithare preferably held to a minimum. Wire bonds can easily introducenano-Henry level inductances into the package if care is not taken. Onemethod to reduce the parasitics of a wire bond is to press the bond flattoward the package 19 or substrate 43 (FIG. 4) This limits the wirecurvature to reduce flux linkage, and brings the wire closer to theground plane to act more as a transmission line with controlledimpedance.

[0039] In particular, wire bonds 40 may be used for coupling thephotodiodes 21 in series, as described above, and wire bonds 41 may beused for coupling the optical power fiber unit 20 to the wirelesscommunications unit 25. Additionally, wire bonds 42 a, 42 b may be usedfor coupling the wireless communications unit 25 to the dipole antennaelements 34 a, 34 b (FIG. 1).

[0040] The wireless communication unit 25 may include a radio frequency(RF) transmitter 27, and an optical signal grating 28 optimized forextracting optical data signals from the fiber 11. Of course, theoptical signal grating 28 and power grating 22 may be optimizeddifferently. According to one important aspect of the invention, the RFtransmitter 27 may be an ultra-wideband (UWB) transmitter. UWB provideswireless communications spread to very low power spectral density acrossa very wide band of frequencies. Data is transmitted by modulating andradiating discrete pulses of RF energy. As a result, UWB may beparticularly advantageous for use in the communication system 10 becauseit may coexist with many existing continuous wave narrowband systemswithout interference. Furthermore, the broad spectral nature and/or lowfrequency content of UWB pulses makes it better suited to penetratewalls and obstacles than other existing technologies. Of course, thoseof skill in the art will appreciate that other forms of wirelesscommunication may also be used in accordance with the present invention.

[0041] As illustratively shown in FIG. 3, for example, theultra-wideband transmitter 27 may include an optical signal detector 26having an input coupled to the signal optical grating (FIG. 2). Thesignal detector 26 may also be a photodiode, such as the InGaAsphotodiode described above. The same considerations described above withrespect to placement, efficiency, etc. of the photodiodes 21 is alsoapplicable to the photodiode 26, and will therefore not be discussedfurther here except to note that typically only one photodiode 26 isrequired for signal detection (although more may be used). Further,optional signal conditioning circuitry (not shown) may also be includedin some embodiments which, in those embodiments where the wirelesscommunication unit 25 is implemented using semiconductor technology, maybe implemented using the same technology.

[0042] An amplifier 30 has an input connected to the output of theoptical detector 26. The transmitter further includes a pseudorandomcode generator 31, a multiplier 32 having inputs connected to theoutputs of the amplifier 30 and the pseudorandom code generator, and apulse generator 33 having an input connected to the output of themultiplier. Other UWB transmitter circuitry arrangements are alsopossible, as will be understood by those of skill in the art.

[0043] The ultra-wideband transmitter 27 may also include an antenna 34connected to the output of the pulse generator 33. By way of example,the antenna 34 may be a dipole antenna connected to the ultra-widebandtransmitter 27 (or other suitable RF device) by wire bonds 42 a, 42 b(FIG. 1). For a particularly compact and efficient construction, thedipole antenna 34 preferably includes first and second portions 34 a, 34b extending in opposite directions along the longitudinal side of theoptical fiber 11, as illustratively shown in FIG. 2.

[0044] To maintain a low profile, it would be preferable to use abroadband dipole antenna 34 that can be integrated onto the side of theoptical fiber. Yet, as will be appreciated by those of skill in the art,most dipole antennas have an inherently narrow band because they areresonant structures that support standing waves. Accordingly, variousapproaches may be used to increase the bandwidth of the dipole antenna34 to support ultra-wideband transmission more efficiently. One suchapproach is the traveling wave approach, in which the currentdistribution in the antenna is altered so that it supports a travelingwave.

[0045] More particularly, the amplitude of the current wave is made todecrease with distance away from the input terminals by using aresistive material to form the dipole. The antenna 34 may be truncatedat the point where the current distribution becomes negligible withoutsignificantly affecting the performance of the antenna. With very littlecurrent to reflect from the dipole endpoints, resonance is avoided andthe structure supports traveling waves. This approach improvesbandwidth, but potentially at the cost of efficiency due to dissipativelosses in the antenna 34. It will be appreciated by those skilled in theart that the resistance profile of the antenna 34 may need to be variedalong its length to optimize the trade-off between efficiency andbandwidth in some applications. Further information regarding thisapproach may be found in Tonn et al., “Traveling Wave Microstrip DipoleAntennas”, I.E.E.E., Electronics Letters, volume 31, issue 24, Nov. 23,1995, pages 2064 to 2066.

[0046] Yet another approach is that of impedance loading, whichpurposely introduces parasitics to broaden the frequency response bymaking the effective length of the dipole frequency dependent. This isaccomplished by preventing higher frequencies from having multipleresonances and confining them to a smaller portion of the dipole. Hereagain, this approach may improve bandwidth at the cost of efficiency dueto dissipative losses in the parasitic loads. Thus, the impedanceprofile of the antenna 34 may need to be varied along its length tooptimize the trade-off between efficiency and bandwidth in someapplications. Further information on this approach may be found in“Numerical modeling and design of loaded broadband wire antennas” byAustin et al., I.E.E.E, Fourth International Conference on HF RadioSystems and Techniques, 1988, pages 125 to 129.

[0047] Accordingly, those skilled in the art may be required todetermine which of the above approaches (or others) may be best suitedfor a particular implementation of the present invention. Furthermore,the impedance and/or resistance profile of the antenna can be tailoredfor reasons other than bandwidth and efficiency. The profile can bedesigned and optimized for functions such as pulse shaping and signalfiltering.

[0048] As noted above, in accordance with one aspect of the presentinvention, the power optical grating 22 is used for extracting lightfrom the core 23 to power the wireless communications unit 25, and theoptical signal grating 28 is used to either extract light from (in thecase of signal transmission from the wireless communications unit) orintroduce light into (i.e., in the case of signal reception by thewireless communications unit) the core. Of course, those of skill in theart will appreciate that other approaches exist for extracting lightfrom an optical fiber 11, such as evanescent coupling, power splitting,or even multiple fibers. Such approaches, as well as other suitableapproaches known to those skilled in the art, are also included withinthe scope of the present invention.

[0049] Preferably, different optical wavelengths are used for poweringand signals in the optical-wireless device 12. More particularly, thewireless communication unit 25 may operate with light having an opticalwavelength λ₂, which is provided (in the case of transmission by thewireless communication unit) by an optical signal source 35 (FIG. 5). Insuch case, the optical signal grating 28 is “tuned” to λ₂, as will bediscussed further below. Further, the communication system 10 mayinclude an optical power source 36 coupled to the optical fiber, and,more particularly, the core 23, for powering the optical fiber powerunit 20 using light having the wavelength λ₁, as noted above. Of course,in some embodiments it may be possible to extract both signals and powerfrom a single source of light having the same wavelength. The opticalpower source 36 and the optical signal source 35 may be circuitryinternal to the server 16, for example.

[0050] Fabrication of the gratings 22 and 28 will now be discussed infurther detail. To facilitate the fabrication process, a fiber bench 29may advantageously be used. A fiber bench is a section of fiber where aportion of the cladding 24 is polished away to form a flat surface inclose proximity to the fiber core 23. It will be appreciated by thoseskilled in the art that the surface gratings 22, 28 fabricated on thefiber bench 29 can exploit the evanescent field to perform a variety offunctions such as spectral filtering, dispersion compensation, modematching, mode stripping, or light extraction and injection. Thegratings 22, 28 can also be designed to perform these functions overselected wavelengths (e.g., λ₁ and λ₂) or modes, while not affectingothers.

[0051] Interfacing with the optical fiber 11 in this manner has theadvantages of lower insertion loss, reduced system complexity, enhancedfunctionality, and the potential for volume production. A conventionalsplice might otherwise suffer from higher losses in the optical fiber 11when using multiple optical-wireless devices 12 operating from differentwavelengths. The fiber bench 29 can also be used as a micro-sizedsubstrate to host small devices such as MEMS, sensors (e.g.,bio/chemical, acoustic, seismic, etc.), or other microsystems in certainembodiments.

[0052] The fiber bench 29 can be formed by placing the fiber in asilicon V-groove and filling the gaps with an epoxy. With the epoxycured, the entire assembly is polished until the cladding 24 of theoptical fiber 11 is within close proximity to the core 23. A liquid droptest measurement may then be used to accurately control the proximity ofthe fiber bench 29 surface to the fiber core 23. The process may beautomated, and systems with fiber benches can potentially be massproduced at low cost. For further details on the use of fiber benches,see, e.g., Leminger and Zengerle, Journal of Lightwave Technology,Volume 3, 1985.

[0053] Additional benefits of this approach include the ability to usethe silicon bench 29 portion of the device for integration with detectorelectronics. Moreover, it is feasible that additional optics and/orantenna elements (not shown) can be integrated on the silicon portion ofthe fiber bench 29, as will be appreciated by those of skill in the art.

[0054] The liquid drop test measurement method assesses the proximity ofthe fiber bench 29 surface to the core 23 of the optical fiber 11. Lightis injected into one end of the optical fiber 11 so that it propagatesthrough the region of the fiber bench 29 and eventually to a powermeter. By placing a drop of liquid on the fiber bench 29 surface, lightis outcoupled in the region of the liquid and can be measured by thepower meter as loss. The fraction of light lost can be used to computethe distance from the bench surface to the core of the fiber.

[0055] One approach for fabricating the gratings 22, 28 involves tiltingthe core 23 during the formation thereof. As will be understood by thoseof skill in the art, gratings are inherently spectrally selective due totheir dispersive properties, and can be designed to selectively redirectbands of wavelengths out of the core 23. The outcoupled light would besubsequently focused onto the photodiodes 21, 26 using micro-opticalelements fabricated on the flat side of the optical fiber 11. Since thisapproach requires photosensitive glass to produce the gratings 22, 28adjacent the core 23, a strong variation in the index may be difficultto realize. A low index modulation requires a long interaction length tocouple large amounts of optical power out of the fiber. This maycomplicate focusing and limit micropackaging options.

[0056] Accordingly, standard lithographic processes may be used tofabricate the surface gratings 22, 28 by etching them onto the polishedsurface of a optical fiber 11. To reduce the interaction length, theindex modulation may be greatly enhanced by applying a higher indexmaterial overcoat on the surface of the grating structure.

[0057] Tilted surface grating structures may also potentially be used tooptimize light extraction and photodiode illumination efficiency. Thiscan be achieved by placing the optical fiber 11 on a tilted fixture andusing an anisotropic etch pattern on the fiber bench 29 surface. Thisapproach can yield slant angles from 0 to 30 degrees, for example. Toavoid the need for additional focusing optics, the interaction length ofthe grating structures 22, 28 is preferably no longer than the activeregions of their respective photodiodes 21, 26. In this manner, theoutcoupled light will be inherently confined to the area of the activeregion. If additional focusing becomes necessary, diffractive optics maybe used to focus light onto the photodiodes 21, 26, as will beunderstood by those skilled in the art.

[0058] The above approach for extracting light is based on redirecting,or tapping, the guided light out of the optical fiber 11 from specificwavelengths, or modes, for power and signal extraction. An alternateapproach views the problem as a spectrally selective directionalcoupler. The fiber core 23 and the photodiode substrate represent thetwo regions for light to propagate. By bringing these two regions inclose proximity, it is possible to couple light from the fiber to thephotodiode very efficiently by designing a spectrally selective gratingto match the propagation constants of these two regions, effectivelyforming a directional coupler, as will be appreciated by those of skillin the art.

[0059] As noted above, light for signals and power may be provided ondifferent wavelengths λ₁, λ₂ and, using the wavelength selectivegratings 22, 28, the power and signal light can thereby be extractedseparately. An alternate approach is to provide the light for signalsand power on different propagating modes. For example, a process hasbeen developed which uses a vortex lens to excite specific modes of agraded-index multimode which may be suitable for this purpose. Thisprocess is described by Johnson et al. in “Diffractive Vortex Lens forMode-Matching Graded Index Fiber,” Optical Society of America, TopicalMeeting on Diffractive and Micro-Optics, 2000. Therefore, it may also befeasible to use diffractive optics to specifically launch light intodifferent spatial modes for the power and signal wavelengths λ₁, λ₂, aswill be appreciated by those skilled in the art. Correspondingly, itwill also be appreciated that diffractive optics may potentially bedesigned for spatially demultiplexing the power and signal modes,respectively.

[0060] Another approach is to utilize a duplex fiber assembly with onefiber devoted to providing power and the other fiber for signaldistribution. This will have some advantages in that the power channelcan be amplified, or re-supplied, at various places in the network,without interrupting the signal fiber. In this manner, the power sourcecan be distributed, which may make the communication system 10 morereliable and robust. Moreover, the optical fiber 11 can be used withwavelength division multiplexing (WDM) or dense WDM (DWDM) schemes, forexample, as will be appreciated by those of skill in the art. Thisapproach can distribute the different signals using standard passive WDMtechnology and standard amplifier technology for the power channel.However, this integration potentially requires a larger amount of realestate than the single optical fiber approach disclosed above. Ofcourse, it will be appreciated that both embodiments are included withinthe scope of the present invention, and that a separate conductive wirecould even be used to provide power in some embodiments.

[0061] As noted above, portions of the optical-wireless device mayadvantageously be implemented in a semiconductor device having apackaging 19 (FIG. 2). In this embodiment, the packaging 19 may serve asa substrate for mounting the optical fiber power unit 20 and thewireless communication unit 25 to the longitudinal side of the opticalfiber 11. In the embodiment illustrated in FIG. 4, a separate substrate43 (e.g., a ceramic substrate) may be used for this purpose as well.

[0062] One potential micropackaging approach illustrated in FIG. 4involves making the various hardware portions modular. Moreparticularly, a row of photodiodes 21, 26 is fixed to the front side ofthe ceramic substrate 43. The back side of the substrate 43 is populatedwith the UWB radio hardware described above. Electrical interconnectionis provided by conductive and resistive epoxies, metal traces in theceramic substrate, and wire bonds, as also noted above. In thisconfiguration, the ceramic and silicon substrates could be “snapped”together, for example.

[0063] It was also noted above that the optical-wireless unit 12 mayboth transmit and receive wireless signals. In those embodiments wherethe wireless communication unit 12 includes a wireless transmitter 27,the communication system 10 may further include at least one wirelessreceiver 37 (and associated antenna 38) spaced from the wirelesstransmitter and receiving signals therefrom, as illustratively shown inFIG. 5. Conversely, in those embodiments where the wirelesscommunication unit 12 includes a wireless receiver, the system may alsoinclude at least one wireless transmitter 60′ (and associated antenna61′) spaced from the wireless receiver and transmitting signals thereto.Of course, in yet other embodiments, duplex communications may beprovided, i.e., the wireless communications unit 12 may include atransceiver, for example.

[0064] Turning now to FIG. 7, a method aspect of the invention foroptical-wireless communication will now be described. The method maybegin (Block 70) with coupling, at Block 71, at least oneoptical-wireless device 12 to a longitudinal side of an optical fiber11, with the at least one optical-wireless device including an opticalfiber power unit 20 and a wireless communication unit 25 connectedthereto, as previously described above. The method may also includesupplying optical power into the optical fiber 11, at Block 72,converting the optical power in the optical fiber into electrical powerusing the optical fiber power unit 20, at Block 74, and electricallypowering the wireless communication unit 25 for optical-wirelesscommunication using the electrical power converted from the opticalpower, at Block 73, thus concluding the method (Block 75). Additionalmethod aspects will be understood from the above description and willtherefore not be discussed further herein.

[0065] It will therefore be appreciated by those of skill in the artthat numerous advantages are provided by the communication system 10 ofthe present invention. In particular, these advantages may include:seamless conversion between optical and wireless domains; reliable,untethered, and high capacity access to optical links; the potentialbenefits of ultra-wideband impulse radio; a high degree of covertness; asmall compact form factor; distributing wireless node functionalityalong the optical fiber 11 without optical-electrical-optical splices;more survivable systems due to added redundancy; more mobile systemsthat are easier to manage than conventional optical-to-wireless systems;less complex systems than conventional optical-to-wireless converters;cabling minimization; systems that may be rapidly deployed at low cost;copperless LANs that are easier and quicker to install than conventionaloptical-to-wireless systems; significant increase in the reach of“conventional” UWB links and ad-hoc networks; latency and processingoverhead may be substantially eliminated at optical/wirelessinterworking points; frequency allocation restraints may be bypassed;and system costs may be reduced.

[0066] Many modifications and other embodiments of the invention willcome to the mind of one skilled in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. Therefore, it is to be understood that the invention is not tobe limited to the specific embodiments disclosed, and that modificationsand embodiments are intended to be included within the scope of theappended claims.

That which is claimed is:
 1. A communication system comprising: anoptical fiber; and at least one optical-wireless device coupled to alongitudinal side of said optical fiber and comprising an optical fiberpower unit coupled to said optical fiber for converting optical powertherein into electrical power, and a wireless communication unitelectrically powered by said optical fiber power unit and coupled tosaid optical fiber.
 2. A communication system according to claim 1wherein said at least one optical-wireless device further comprises asubstrate mounting said optical fiber power unit and said wirelesscommunication unit to the longitudinal side of said optical fiber.
 3. Acommunication system according to claim 1 wherein said optical fiberpower unit comprises a photovoltaic device and a power optical gratingcoupling said photovoltaic device to the longitudinal side of saidoptical fiber.
 4. A communication system according to claim 1 whereinsaid wireless communication unit comprises a radio frequency transmitterand a signal optical grating coupling said radio frequency transmitterto the longitudinal side of said optical fiber.
 5. A communicationsystem according to claim 4 wherein said radio frequency transmittercomprises an ultra-wideband transmitter.
 6. A communication systemaccording to claim 5 wherein said ultra-wideband transmitter comprises:an optical detector having an input coupled to said signal opticalgrating and having an output; an amplifier having an input connected tothe output of said optical detector and having an output; a pseudorandomcode generator having an output; a multiplier having inputs connected tothe outputs of said amplifier and pseudorandom code generator, andhaving an output; a pulse generator having an input connected to theoutput of said multiplier, and having an output; and an antennaconnected to the output of said pulse generator.
 7. A communicationsystem according to claim 6 wherein said antenna comprises a dipoleantenna.
 8. A communication system according to claim 7 wherein saiddipole antenna comprises first and second portions extending in oppositedirections along the longitudinal side of said optical fiber.
 9. Acommunication system according to claim 1 wherein said optical fibercomprises a core and a cladding surrounding said core; and wherein saidoptical fiber power unit and said wireless communication unit arecoupled to said core.
 10. A communication system according to claim 1wherein said wireless communication unit comprises a wirelesstransmitter; and further comprising at least one wireless receiverspaced from said wireless transmitter and receiving signals therefrom.11. A communication system according to claim 1 wherein said wirelesscommunication unit comprises a wireless receiver; and further comprisingat least one wireless transmitter spaced from said wireless receiver andtransmitting signals thereto.
 12. A communication system according toclaim 1 wherein said at least one optical-wireless device comprises aplurality of optical-wireless devices coupled to said optical fiber atspaced apart locations along the longitudinal side of said opticalfiber.
 13. A communications system according to claim 1 wherein saidwireless communication unit operates at a first optical wavelength; andfurther comprising an optical power source coupled to said optical fiberfor powering said optical fiber power unit and operating at a secondwavelength different than the first optical wavelength.
 14. Anoptical-wireless device to be coupled to a longitudinal side of anoptical fiber and comprising: a substrate for coupling to thelongitudinal side of the optical fiber; an optical fiber power unitcarried by said substrate to be coupled to said optical fiber forconverting optical power therein into electrical power; and a wirelesscommunication unit carried by said substrate, electrically powered bysaid optical fiber power unit, and to be coupled to the optical fiber.15. An optical-wireless device according to claim 14 wherein saidoptical fiber power unit comprises a photovoltaic device and a poweroptical grating for coupling said photovoltaic device to the opticalfiber.
 16. An optical-wireless device according to claim 14 wherein saidwireless communication unit comprises a radio frequency transmitter anda signal optical grating for coupling said radio frequency transmitterto the optical fiber.
 17. An optical-wireless device according to claim16 wherein said radio frequency transmitter comprises an ultra-widebandtransmitter.
 18. An optical-wireless device according to claim 17wherein said ultra-wideband transmitter comprises: an optical detectorhaving an input coupled to said second optical grating and having anoutput; an amplifier having an input connected to the output of saidoptical detector and having an output; a pseudorandom code generatorhaving an output; a multiplier having inputs connected to the outputs ofsaid amplifier and pseudorandom code generator, and having an output; apulse generator having an input connected to the output of saidmultiplier, and having an output; and an antenna connected to the outputof said pulse generator.
 19. An optical-wireless device to be coupled toa longitudinal side of an optical fiber and comprising: a substrate tobe coupled to the longitudinal side of the optical fiber; a wirelesscommunication unit carried by said substrate and to be coupled to theoptical fiber; and an antenna connected to said wireless communicationunit and to be carried by the optical fiber.
 20. An optical-wirelessdevice according to claim 19 wherein said antenna comprises a dipoleantenna.
 21. An optical-wireless device according to claim 20 whereinsaid dipole antenna comprises first and second portions to extend inopposite directions along the longitudinal side of the optical fiber.22. An optical-wireless device according to claim 19 wherein saidwireless communication unit comprises a radio frequency transmitter anda signal optical grating for coupling said radio frequency transmitterto the optical fiber.
 23. An optical-wireless device according to claim22 wherein said radio frequency transmitter comprises an ultra-widebandtransmitter.
 24. An optical-wireless device according to claim 23wherein said ultra-wideband transmitter comprises: an optical detectorhaving an input coupled to said optical grating and having an output; anamplifier having an input connected to the output of said opticaldetector and having an output; a pseudorandom code generator having anoutput; a multiplier having inputs connected to the outputs of saidamplifier and pseudorandom code generator, and having an output; and apulse generator having an input connected to the output of saidmultiplier, and having an output connected to said antenna.
 25. Anoptical-wireless device to be coupled to an optical fiber andcomprising: a substrate to be coupled to the optical fiber; and anultra-wideband wireless communication unit carried by said substrate andto be coupled to the optical fiber.
 26. An optical-wireless according toclaim 25 wherein said substrate is to be coupled to a longitudinal sideof the optical fiber.
 27. An optical-wireless according to claim 25wherein said ultra-wideband communication unit comprises anultra-wideband transmitter and a signal optical grating for couplingsaid ultra-wideband transmitter to the optical fiber.
 28. Anoptical-wireless device according to claim 27 wherein saidultra-wideband transmitter comprises: an optical detector having aninput coupled to said signal optical grating and having an output; anamplifier having an input connected to the output of said opticaldetector and having an output; a pseudorandom code generator having anoutput; a multiplier having inputs connected to the outputs of saidamplifier and said pseudorandom code generator, said multiplier alsohaving an output; a pulse generator having an input connected to theoutput of said multiplier, and having an output; and an antenna to becarried by the optical fiber and connected to the output of said pulsegenerator.
 29. An optical-wireless device according to claim 28 whereinsaid antenna comprises a dipole antenna.
 30. An optical-wireless deviceaccording to claim 29 wherein said dipole antenna comprises first andsecond portions to extend in opposite directions along the longitudinalside of the optical fiber.
 31. A method for optical-wirelesscommunication comprising: coupling at least one optical-wireless deviceto a longitudinal side of an optical fiber, the at least oneoptical-wireless device comprising an optical fiber power unit and awireless communication unit connected thereto; supplying optical powerinto the optical fiber; converting the optical power in the opticalfiber into electrical power using the optical fiber power unit; andelectrically powering the wireless communication unit foroptical-wireless communication using the electrical power converted fromthe optical power.
 32. A method according to claim 31 wherein theoptical-wireless device further comprises a substrate carrying theoptical fiber power unit and the wireless communication unit; andwherein coupling comprises coupling the substrate to the longitudinalside of the optical fiber.
 33. A method according to claim 31 whereinthe wireless communication unit comprises a radio frequency transmitterand a signal optical grating coupling the radio frequency transmitter tothe longitudinal side of the optical fiber.
 34. A method according toclaim 33 wherein the radio frequency transmitter comprises anultra-wideband transmitter.
 35. A method according to claim 31 whereinthe optical-wireless communication device further comprises a dipoleantenna including first and second portions; and wherein couplingcomprises mounting the first and second portions to extend in oppositedirections along the longitudinal side of the optical fiber.
 36. Amethod according to claim 31 wherein the optical fiber comprises a coreand a cladding surrounding the core; and wherein coupling comprisescoupling the optical fiber power unit and the wireless communicationunit to the core.
 37. A method according to claim 31 wherein thewireless communication unit operates at a first optical wavelength; andwherein supplying optical power comprises supplying optical power at asecond wavelength different than the first optical wavelength.